Hydrogen storage alloy electrode and manufacturing method of the same

ABSTRACT

A hydrogen storage alloy electrode for use in electrochemical hydrogen storage cells, the electrode being in the form of a negative electrode fabricated by sintering a mixture of a hydrogen storage alloy containing manganese and an alloy containing a measured amount of manganese.

RELATED APPLICATIONS

This application is a continuation-in-part of our earlier applicationSer. No. 08/717,115 filed Sep. 20, 1996, now U.S. Pat. No. 5,766,792.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydrogen storage alloy electrodecapable of reversibly electrochemically storing and discharginghydrogen. More particularly, the present invention relates to a hydrogenstorage alloy negative electrode of the sintered type and amanufacturing method of the same.

2. Description of the Prior Art

In recent advances of electronic technology, development of compact andlightweight high performance secondary batteries of higher energydensity is strongly required as a power source for portable cordlesselectronic equipment. In such requirement, metal hydride batteries usinga hydrogen storage alloy negative electrode has been particularlynoticed as a more environmentally clean energy source rather thanlead-acid, nickel-cadmium or other batteries.

A conventional hydrogen storage alloy negative electrode of thenon-sintering type for alkaline cells is manufactured by the steps ofmixing powdered hydrogen storage alloy materials with binder agents suchas polyethylene oxide, polyvinyl alcohol or the like and coating aslurry of the mixture on a conductive core plate such as a perforated(punched) metal plate. In the hydrogen storage alloy negative electrode,the binder agents must be interposed between particles of the hydrogenstorage alloy materials and between the hydrogen storage alloy and theconductive core plate to retain the hydrogen storage alloy on theconductive core plate. The discharge characteristics and capacity of thehydrogen storage alloy negative electrode are deteriorated due toinsulation resistance of the binder agents.

To solve the problem, there has been proposed a manufacturing method ofa hydrogen storage alloy negative electrode of the sintering type, forexample, in Japanese Patent Publication No. 58(1983)-46827, JapanesePatent Laid-open Publication No. 2(1990)-12765, etc. The manufacturingmethod disclosed therein comprises the steps of mixing powdered hydrogenstorage alloy materials with powders of precursor materials, such as Co,Ni, TiNi_(x) and the like, subjecting the mixture of the powdermaterials placed on a perforated metal plate to a compaction process andsintering the mixture on the metal plate in a vacuum or an inertenvironment to provide a sintered hydrogen storage alloy negativeelectrode of higher strength.

In the manufacturing process of the negative electrode, however, whenthe hydrogen storage alloy materials containing a measured amount ofmanganese are sintered after being mixed with the powders of Co, Ni,TiNi_(x), the manganese melts out of the hydrogen storage alloy,resulting in degradation of the composition of the hydrogen storagealloy. This decreases the discharge capacity of the negative electrode.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to providean electrochemical hydrogen storage alloy negative electrode and amanufacturing method for the same capable of reducing degradation of thehydrogen storage alloy composition.

According to the present invention, this object is accomplished byproviding a hydrogen storage alloy electrode for use in electrochemicalhydrogen storage cells, the electrode being in the form of a negativeelectrode fabricated by sintering a mixture of a hydrogen storage alloycontaining manganese and an alloy containing a measured amount ofmanganese.

According to an aspect of the present invention, there is provided amethod of manufacturing a hydrogen storage alloy electrode for use as anegative electrode in electrochemical hydrogen storage cells, the methodcomprising the steps of increasing an amount of manganese contained inpowdered hydrogen storage alloy materials having a desired composition,mixing nickel-metal or a compound of nickel with the powdered hydrogenstorage alloy materials, and sintering a mixture of the powderedhydrogen storage alloy materials and the nickel-metal or the compound ofnickel in an inert atmosphere or a reduced atmosphere.

According to another aspect of the present invention, there is provideda method of manufacturing a hydrogen storage alloy electrode for use asa negative electrode in electrochemical hydrogen storage cells, themethod comprising the steps of preparing a measured amount of powderedhydrogen storage alloy materials having a desired composition includinga measured amount of manganese, mixing powder of a Mn--Ni or Mn--Fealloy with the powdered hydrogen storage alloy materials, preparing aslurry of a mixture of the powder of the Mn--Ni or Mn--Fe alloy and thepowdered hydrogen storage alloy materials and coating the slurry on acore plate, compacting the mixture on the core plate after drying, andsintering the mixture on the core plate in an environment of mixed gasesof hydrogen and argon.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will bemore readily appreciated from the following detailed description ofpreferred embodiments thereof when taken together with the accompanyingdrawing, which illustrates discharge capacities in relation to adischarge rate (at design rate of 1000 mAh).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments and their comparative embodiments of hydrogenstorage alloys having a desired composition represented by the formula"MmNi₃.70 Co₀.60 Mn₀.60 Al₀.20 " will be described hereinafter.

EXAMPLE 1

An amount of a compound of nickel, cobalt, manganese and aluminummeasured at a ratio of 1:3.7:0.6:0.6:0.2 in their element forms wasmixed and subjected to an argon atomizing process to fabricate a solidingot of hydrogen storage alloy having the composition represented bythe formula "MmNi₃.70 Co₀.60 Mn₀.60 Al₀.20 ". The ingot of hydrogenstorage alloy was mechanically comminuted, and the resulting powders ofmore than 150 μm and less than 25 μm in particle diameter were removedby mesh passage to yield powdered hydrogen storage alloy materials ofabout 80 μm in mean particle diameter.

To fabricate a sintered hydrogen storage alloy negative electrode, amethanol solution of manganese acetylacetone containing nickel powderwas heated at a temperature of approximately 260° centigrade to adherethe manganese to the nickel powder at a ratio of about 2:1 thereby toyield mixed powders of a Mn--Ni alloy. The mixed powders of the Mn--Nialloy were mixed with the powdered hydrogen storage alloy materials at aweight ratio of 1:9 and an amount of aqueous solution of 2 wt %polyethylene oxide was added as a paste agent to the mixture of theMn--Ni alloy powders and hydrogen storage alloy materials at a ratio of0.5:1 to prepare a slurry. The slurry of the mixture was coated on anickel plated metallic perforated core plate and dried. Thereafter, themixture of the two powders was compacted at a pressure rate of 10% toenhance the packing density and subjected to a reducing heat treatmentfor one hour at approximately 900° centigrade in an environment of mixedgases of hydrogen and argon (4 vol % hydrogen). The hydrogen storagealloy electrode of the sintered type manufactured by the foregoingprocess is called sample "a" hereinafter. After the heat treatment, thecomposition of the sample "a" was inspected by electron probemicroanalysis (EPMA). As a result of the inspection, it was found thatthe composition of the sample "a" was represented by the formula:MmNi₃.71 Co₀.60 Mn₀.59 Al₀.20. The segregation in the sample "a" wassubstantially the same before the heat treatment of the mixture of thetwo powders.

EXAMPLE 2

Powder of 10 wt % MnNi₂ was mixed with the powdered hydrogen storagealloy materials fabricated in the same manner as in EXAMPLE 1, and anaqueous solution of polyethylene oxide was added to the mixture of thepowders of MnNi₂ and hydrogen storage alloy materials to prepare aslurry. The slurry of the mixture was coated on a nickel plated metallicperforated core plate and dried. Thereafter, the mixture of the twopowders was compacted at a pressure rate of 10% to enhance the packingdensity and subjected to a reducing heat treatment for one hour atapproximately 900° centigrade in an environment of mixed gases ofhydrogen and argon (4 vol % hydrogen). The hydrogen storage alloyelectrode of the sintering type manufactured by the foregoing process iscalled sample "b" hereinafter. After the heat treatment, the compositionof the sample "b" was inspected by electron probe microanalysis (EPMA).As a result of the inspection, it was found that the composition of thehydrogen storage alloy electrode "b" was represented by the formula:

MmNi₃.70 Co₀.60 Mn₀.60 Al₀.20. The segregation in the hydrogen storagealloy electrode "b" was substantially the same before the heat treatmentof the mixture of the powders of MnNi₂ and hydrogen storage alloymaterial.

EXAMPLE 3

Powder of MnCl₂, Fe₂ O₃ and carbon was mixed with the powdered hydrogenstorage alloy materials prepared in the same manner as in EXAMPLE 1 at aweight ratio of 0.5:0.5:0.5:9, and an aqueous solution of polyethyleneoxide was added to the mixture of the two powders to prepare a slurry.The slurry of the mixture was coated on a nickel plated metallicperforated core plate and dried. Thereafter, the mixture of the twopowders was compacted at a pressure rate of 10% to enhance the packingdensity and subjected to a reducing heat treatment for one hour atapproximately 900° centigrade in an environment of mixed gases ofhydrogen and argon (4 vol % hydrogen). The hydrogen storage alloyelectrode of the sintering type manufactured by the foregoing process iscalled sample "c" hereinafter. After the heat treatment, the compositionof the hydrogen storage alloy electrode "c" was inspected by electronprobe microanalysis (EPMA). As a result of the inspection, it was foundthat the composition of the hydrogen storage alloy electrode "c" wasrepresented by the formula: MmNi₃.71 Co₀.60 Mn₀.59 Al₀.20. Thesegregation in the hydrogen storage alloy electrode "c" wassubstantially the same before the heat treatment of the mixture of thepowders of MnCl₂, Fe₂ O₃ and carbon and powdered hydrogen storage alloymaterial.

EXAMPLE 4

Powder of 10 wt % MnFe₂ was mixed with the powdered hydrogen storagealloy materials prepared in the same manner as in EXAMPLE 1, and anaqueous solution of polyethylene oxide was added to the mixture of thetwo powders to prepare a slurry. The slurry of the mixture was coated ona nickel plated metallic perforated core plate and dried. Thereafter,the mixture of the two powders was compacted at a pressure rate of 10%to enhance the packing density and subjected to a reducing heattreatment for one hour at approximately 900° centigrade in anenvironment of mixed gases of hydrogen and argon (4 vol % hydrogen). Thehydrogen storage alloy electrode of the sintering type manufactured bythe foregoing process is called sample "d" hereinafter. After the heattreatment, the composition of the hydrogen storage alloy electrode "d"was inspected by electron probe microanalysis. As a result of theinspection, it was found that the composition of the sample "d" wasrepresented by the formula: MmNi₃.70 Co₀.60 Mn₀.60 Al₀.20. Thesegregation in the sample "d" was substantially the same before the heattreatment of the mixture of the powders of MnFe₂ and hydrogen storagealloy material.

COMPARATIVE EXAMPLE 1

Powdered hydrogen storage alloy materials having the composition:MmNi₃.70 Co₀.60 Mn₀.60 Al₀.20 were prepared in the same manner as inEXAMPLE 1. Powder of 10 wt % metal-nickel was mixed with the powderedhydrogen storage alloy materials, and an aqueous solution ofpolyethylene oxide was added to the mixture of the two powders toprepare a slurry. The slurry of the mixture was coated on a nickelplated metallic perforated core plate and dried. Thereafter, the mixtureof the two powders was compacted at a pressure rate of 10% to enhancethe packing density and subjected to a reducing heat treatment for onehour at approximately 900° centigrade in an environment of mixed gasesof hydrogen and argon (4 vol % hydrogen). The hydrogen storage alloyelectrode of the sintering type manufactured by the foregoing process iscalled comparative sample "e" hereinafter. After the heat treatment, thecomposition of the comparative sample "e" was inspected by electronprobe microanalysis. As a result of the inspection, it was found thatthe composition of the sample "e" was represented by the formula:MmNi₃.77 Co₀.60 MNn₀.28 Al₀.20. In the composition of the sample "e",the amounts of cobalt and aluminum were substantially the same as in thehydrogen storage alloy before the heat treatment, and the amount ofnickel slightly increased from 3.70 to 3.77. However, the amount ofmanganese noticeably decreased from 0.60 to 0.28. This causes internalsegregation of the manganese, resulting in non-uniformities in thecomposition of the hydrogen storage alloy. In this respect, it isassumed that the internal segregation in the hydrogen storage alloy wascaused by the transfer of the manganese into the nickel powder adjacentthe particle surfaces of the hydrogen storage alloy materials during thesintering process.

COMPARATIVE EXAMPLE 2

Powdered hydrogen storage alloy materials having the composition:MmNi₃.70 Co₀.60 Mn₀.60 Al₀.20 were prepared in the same manner as inEXAMPLE 1. Powder of 10 wt % TiNi was mixed with the powdered hydrogenstorage alloy materials, and an aqueous solution of polyethylene oxidewas added to the mixutre of the two powders to prepare a slurry. Theslurry of the mixture was coated on a nickel plated metallic perforatedcore plate and dried. Thereafter, the mixture of the two powders wascompacted at pressure rate of 10% to enhance the packing density thereofand subjected to a reducing heat treatment for one hour at approximately900° centigrade in an environment of mixed gases of hydrogen and argon(4 vol % hydrogen). The hydrogen storage alloy electrode of thesintering type manufactured by the foregoing process is calledcomparative sample "f" hereinafter.

After the heat treatment, the composition of the comparative sample "f"was inspected by electron probe microanalysis (EPMA). As a result of theinspection, it was found that the composition of the sample "f" wasrepresented by the formula: MmNi₃.81 Co₀.61 Mn₀.32 Al₀.21. In thecomposition of the sample "f", the amounts of cobalt and aluminum weresubstantially the same as in the hydrogen storage alloy before the heattreatment, and the amount of nickel slightly increased from 3.70 to3.81. However, the amount of manganese noticeably decreased from 0.60 to0.32. This causes internal segregation of the manganese, resulting innon-uniformities in the composition of the hydrogen storage alloy. Inthis respect, it is assumed that during the sintering process, theinternal segregation in the hydrogen storage alloy was caused bytransfer of the manganese into the powders of TiNi alloy adjacent theparticle surfaces of the hydrogen storage alloy materials.

COMPARATIVE EXAMPLE 3

Powdered hydrogen storage alloy materials having the composition:MnNi₃.70 Co₀.60 Mn₀.60 Al₀.20 were prepared in the same manner as inEXAMPLE 1. An amount of aqueous solution of 2 wt % polyethylene oxidewas added to the powdered hydrogen storage alloy materials at a weightratio of 0.5:1 to prepare a slurry thereof. The slurry of the powderedhydrogen storage alloy material was coated on a nickel plated metallicperforated core plate and dried. Thereafter, the hydrogen storage alloymaterial was compacted at a pressure rate of 10% to enhance the packingdensity thereof and subjected to a reducing heat treatment for one hourat approximately 900° centigrade in an environment of mixed gases ofhydrogen and argon (4 vol % hydrogen). The hydrogen storage alloyelectrode of the sintering type manufactured by the foregoing process iscalled comparative sample "g" hereinafter.

CHARACTERISTIC TEST

(Test 1)

Hydrogen rechargeable secondary cells using the samples "a"-"g" as anegative electrode and a conventional nickel hydroxide electrode of thesintering type as a positive electrode were tested. In the manufactureof the secondary cells, the negative and positive electrodes weredisposed in a housing and opposed to one another through a separatortherebetween. Thereafter, the housing was filled with a sufficientamount of 30 wt % KOH solution and sealed to provide a hydrogen storagerechargeable secondary cell of nominal capacity 300 mAh. In the tests,the secondary cells each were charged at 30 mA for sixteen hours. Afterrested for one hour, the secondary cells each were discharged at 60 mAuntil the voltage becomes 1.OV to measure the discharge capacity. Theresults are illustrated in the following Table (1). Provided that, thedischarge capacity of the comparative sample "g" is represented by "100"in the Table (1).

                  TABLE 1    ______________________________________              Composition of hydrogen storage                                 Discharge    Electrode alloy (After sintering)                                 capacity    ______________________________________    a         MmNi.sub.3.71 Co.sub.0.60 Mn.sub.0.59 Al.sub.0.20                                 102    b         MmNi.sub.3.70 Co.sub.0.60 Mn.sub.0.60 Al.sub.0.20                                 102    c         MmNi.sub.3.71 Co.sub.0.60 Mn.sub.0.59 Al.sub.0.20                                 101    d         MmNi.sub.3.70 Co.sub.0.60 Mn.sub.0.60 Al.sub.0.20                                 102    e         MmNi.sub.3.77 Co.sub.0.60 Mn.sub.0.28 Al.sub.0.20                                 52    f         MmNi.sub.3.81 Co.sub.0.61 Mn.sub.0.32 Al.sub.0.21                                 60    ______________________________________

From the Table (1), it is apparent that the discharge capacity of eachof the samples "a", "b", "c" and "d" becomes higher than that of thecomparative samples "e" and "f". Since in the samples "a"-"d", an alloycontaining a measured amount of manganese or a compound of manganese wasmixed with the powdered hydrogen storage alloy materials and sintered,the composition of the hydrogen storage alloy is maintained as in thedesired composition without causing any degradation thereof even if themanganese melts out of the hydrogen storage alloy during the sinteringprocess. In addition, the melted manganese is integrated withnickel-metal to form a MnNi-metal superior in conductivity.

On the other hand, the hydrogen storage alloys in the comparativesamples "e" and "f" were mixed with nickel-metal, TiNi withoutcontaining any manganese. As a result, the manganese melts out of thehydrogen storage alloy during the sintering process, resulting indegradation of the composition of the hydrogen storage alloy.

(Test 2)

Nickel hydrogen batteries using the samples "a"-"g" as a negativeelectrode and a conventional nickel hydroxide electrode of the sinteringtype as a positive electrode were tested. In the manufacture of thebatteries, the negative and positive electrodes were wound spirallythrough a separator fabricated of non-woven polypropylene and disposedwithin a housing. Thereafter, the housing was filled with a sufficientamount of electrolyte of 30 wt % KOH and sealed to provide a nickelhydrogen battery of nominal capacity 1000 mAh in a single size.Hereinafter, the nickel hydrogen batteries using the samples "a"-"d" arecalled batteries A, B, C and D of the present invention, while thenickel hydrogen batteries using the samples "e", "f" and "g" are calledcomparative batteries E, F and G.

In this test, the discharge rate dependency of each of the batteries A-Gwas measured. For measurement of the discharge rate dependency, thebatteries A-G were charged at 100 mA for sixteen hours. After rested forone hour, the batteries A-G were discharged respectively at 200 mA, 1000mA and 2000 mA until the voltage becomes 1.0V to measure the dischargecapacity. The results are illustrated in the single FIGURE. From thecharacteristic lines illustrated in the FIGURE, it is apparent that eachdischarge capacity of the comparative batteries E and F respectivelymixed with Ni or TiNi in the sintering process becomes small incomparison with the discharge capacity of the comparative battery Gwhile each discharge capacity of the batteries A-D using the alloycontaining a measured amount of manganese or the compound of manganesebecomes larger than the discharge capacity of the comparative battery G.Particularly, it is noted that the discharge capacity of each of thebatteries A-D at 2C (2000 mA) is considerably superior than that of thecomparative batteries E-G.

Although in the embodiments described above, Ni or Fe was used as ametal other than the manganese to be mixed with the hydrogen storagealloy, Co, Al or Cu may be used or at least one metal chosen from thegroup consisting of Ni, Fe, Co, Al and Cu may be used.

In practical embodiments of the present invention, it has been foundthat the composition of the hydrogen storage alloy may be modified as inadditional examples described below.

EXAMPLE (A)

The hydrogen storage alloy was prepared in the form of powdered hydrogenstorage alloy materials having the composition represented by theformula "MmNi₃.70 Co₀.60 Mn_(x) Al₀.8-x ". In the formula, the component"x" was determined in a range of more than 0.1 and less than 0.8 aslisted in the following Table (2). In this example, powder of 10 wt %MnNi₂ was mixed with the powdered hydrogen storage alloy materials, andthe mixture of the powders was subjected to a reducing heat treatmentfor one hour at approximately 900° centigrade in the same manner as inthe Example 1. After the heat treatment, it was found that thecomposition of the hydrogen storage alloy was maintained in the desiredcomposition without causing any degradation thereof. The electrochemicalcapacity of a negative electrode using the hydrogen storage alloy wassubstantially the same as that of the composition "MmNi₃.70 Co₀.60Mn_(x) Al₀.8-x ".

In the case that powder of 10 wt % metal-nickel was mixed with thepowdered hydrogen storage alloy materials instead of the powders ofMnNi₂, transfer of the manganese into the nickel particles adjacent theparticle surfaces of the hydrogen storage alloy materials was observedduring the sintering process, resulting in a decrease of the dischargecapacity of the negative electrode as shown in the following Table (2).

                  TABLE (2)    ______________________________________                                            Discharge    X      Mm     Ni       Co   Mn     Al   capacity    ______________________________________    0.1    1.00   3.70     0.60 0.01   0.70 80    0.2    1.00   3.70     0.60 0.02   0.60 74    0.3    1.00   3.70     0.60 0.06   0.50 70    0.4    1.00   3.70     0.60 0.17   0.40 65    0.5    1.00   3.70     0.60 0.24   0.30 60    0.6    1.00   3.70     0.60 0.28   0.20 52    0.7    1.00   3.70     0.60 0.47   0.10 55    0.8    1.00   3.70     0.60 0.58   0.00 61    ______________________________________

In the Table (2), the discharge capacity is a comparative value in thecase that the discharge capacity of the negative electrode manufacturedby the present invention is defined as 100.

EXAMPLE (B)

The hydrogen storage alloy was prepared in the form of powdered hydrogenstorage alloy materials having the composition represented by theformula "MmNi₃.40 Co₀.80 Mn_(x) Al₀.8-x ". In the formula, the component"x" was determined in a range of more than 0.1 and less than 0.8 aslisted in the following Table (3). In this example, an amount of powdersof 10 wt % MnNi₂ was mixed with the powdered hydrogen storage alloymaterial, and the mixture of the powders was subjected to a reducingheat treatment for one hour at approximately 900° centigrade in the samemanner as in the Example 1. After the heat treatment, it was found thatthe composition of the hydrogen storage alloy was maintained in thedesired composition without causing any degradation thereof. Theelectrochemical capacity of a negative electrode using the hydrogenstorage alloy was substantially the same as that of the composition"MmNi₃.40 Co₀.60 Mn_(x) Al₀.8-x ".

In the case that an amount of powders of 10 wt % metal-nickel was mixedwith the powdered hydrogen storage alloy materials instead of thepowders of MnNi₂, transfer of the manganese into the nickel particlesadjacent the particle surfaces of the hydrogen storage alloy materialswas observed during the sintering process, resulting in a decrease ofthe discharge capacity of the negative electrode as shown in thefollowing Table (3).

                  TABLE (3)    ______________________________________                                            Discharge    X      Mm     Ni       Co   Mn     Al   Capacity    ______________________________________    0.1    1.00   3.40     0.80 0.01   0.70 82    0.2    1.00   3.40     0.80 0.02   0.60 75    0.3    1.00   3.40     0.80 0.07   0.50 70    0.4    1.00   3.40     0.80 0.16   0.40 65    0.5    1.00   3.40     0.80 0.25   0.30 60    0.6    1.00   3.40     0.80 0.35   0.20 52    0.7    1.00   3.40     0.80 0.44   0.10 58    0.8    1.00   3.40     0.80 0.56   0.00 63    ______________________________________

In the Table (3), the discharge capacity is a comparative value in thecase that the discharge capacity of the negative electrode manufacturedby the present invention is defined as 100.

EXAMPLE (C)

An amount of powders of 10 wt % MnNi₂ was mixed with an amount ofpowders of ZrMn₂, and an aqueous solution of polyethylene oxide wasadded to the mixture of the powders of MnNi₂ and ZrMn₂ to prepare aslurry. The slurry of the mixture was coated on a nickel plated metallicperforated core plate and dried. Thereafter, the mixture of the powderswas compacted at a pressure rate of 10% and subjected to a reducing heattreatment for one hour at approximately 900° centigrade in anenvironment of mixed gases of hydrogen and argon (4 vol % hydrogen).After the heat treatment, the composition of a hydrogen storage alloyelectrode of the sintering type manufactured by the foregoing processwas inspected by electron probe microanalysis (EPMA). As a result of theinspection, it was found that the composition of the hydrogen storagealloy was maintained in the desired composition without causing anydegradation thereof.

In the case that powders of 10 wt % metal-nickel was mixed with thepowders of ZrMn₂ instead of the powders of MnNi₂, the composition of thehydrogen storage alloy electrode changed to ZrMn₁.87 as shown in thefollowing Table (4), and the metal-nickel was alloyed with the manganeseMn.

                  TABLE 4    ______________________________________                                  Discharge    Mixed metal               Zr          Mn     capacity    ______________________________________    MnNi2      1.00        2.00   100    Ni         1.00        1.87   66    ______________________________________

EXAMPLE (D)

An amount of powders of 10 wt % MnNi₂ was mixed with an amount ofpowders of TiMn₁.5, and an aqueous solution of polyethylene oxide wasadded to the mixture of the powders of MnNi₂ and TiMn₁.5 to prepare aslurry. The slurry of the mixture was coated on a nickel plated metallicperforated core plate and dried. Thereafter, the mixture of the powderswas compacted at a pressure rate of 10% and subjected to a reducing heattreatment for one hour at approximately 900° centigrade in anenvironment of mixed gases of hydrogen and argon (4 vol % hydrogen).After the heat treatment, the composition of a hydrogen storage alloyelectrode of the sintering type manufactured by the foregoing processwas inspected by electron probe microanalysis (EPMA). As a result of theinspection, it was found that the composition of the hydrogen storagealloy was maintained in the desired composition without causing anydegradation thereof.

In the case that an amount of powders of 10 wt % metal-nickel was mixedwith the powders of TiMn₁.5 instead of the powders of MnNi₂, thecomposition of the hydrogen storage alloy electrode changed to TiMn₁.39as shown in the following Table (5), and the metal-nickel was alloyedwith the manganese Mn.

                  TABLE 5    ______________________________________                                  Discharge             Ti            Mn     capacity    ______________________________________    MnNi2    1.00          1.50   100    Ni       1.00          1.39   76    ______________________________________

What is claimed is:
 1. A hydrogen storage alloy electrode for use inelectrochemical hydrogen storage cells, said electrode being in the formof a negative electrode fabricated by sintering a mixture of powderedhydrogen storage alloy materials having a composition represented by theformula "MmNi₃.70 Co₀.60 Mn_(x) Al₀.8-x " where the component x isdetermined in a range of more than 0.1 and less than 0.8 and an alloycontaining a measured amount of manganese, wherein a portion of Ni inthe storage alloy materials is substituted for the manganese.
 2. Ahydrogen storage alloy electrode as claimed in claim 1, wherein thealloy containing a measured amount of manganese is a Mn--Ni alloy.
 3. Ahydrogen storage alloy electrode for use in electrochemical hydrogenstorage cells, said electrode being in the form of a negative electrodefabricated by sintering a mixture of powdered hydrogen storage alloymaterials having a composition represented by the formula "MmNi₃.40Co₀.80 Mn_(x) Al₀.8-x " where the component x is determined in a rangeof more than 0.1 and less than 0.8 and an alloy containing a measuredamount of manganese, wherein a portion of Ni in the storage alloymaterials is substituted for the manganese.
 4. A hydrogen storage alloyelectrode as claimed in claim 3, wherein the alloy containing a measuredamount of manganese is a Mn--Ni alloy.
 5. A hydrogen storage alloyelectrode for use in electrochemical hydrogen storage cells, saidelectrode being in the form of a negative electrode fabricated bysintering a mixture of powders of a Zr--Mn alloy and an alloy containinga measured amount of manganese.
 6. A hydrogen storage alloy electrode asclaimed in claim 5, wherein the alloy containing a measured amount ofmanganese is a Mn--Ni alloy.
 7. A hydrogen storage alloy electrode foruse in electrochemical hydrogen storage cells, said electrode being inthe form of a negative electrode fabricated by sintering a mixture ofpowders of a Ti--Mn alloy and an alloy containing a measured amount ofmanganese.
 8. A hydrogen storage alloy electrode as claimed in claim 7,wherein the alloy containing a measured amount of manganese is a Mn--Nialloy.
 9. A hydrogen storage alloy electrode for use in electrochemicalhydrogen storage cells, said electrode being in the form of a negativeelectrode fabricated by sintering a mixture of a hydrogen storage alloycontaining manganese and an alloy containing a measured amount ofmanganese.